Curable organopolysiloxane compositions curable by a hydrosilylation reaction are used as protective or coating agents in the manufacture of semiconductor parts of optical semiconductor devices, such as photo-couplers, light-emitting diodes, solid state imaging elements, etc. Since the light received by the optical elements or emitted from these elements passes through the layers of the aforementioned protective or coating agents, it is required that they should neither absorb nor dissipate the light.
The curable organopolysiloxane composition that after curing by a hydrosilylation reaction forms a cured product having high transmittance and index of refraction can be exemplified, e.g., by a curable organopolysiloxane composition comprising: a branched-chain organopolysiloxane that contains phenyl and alkenyl groups; an organohydrogenpolysiloxane that contains in one molecule at least two silicon-bonded hydrogen atoms; and a hydrosilylation catalyst (see Japanese Unexamined Patent Application Publication (hereinafter referred to as “Kokai”) H 11-1619). Another example is a curable organopolysiloxane composition comprising: a diorganopolysiloxane that contains in one molecule at least two alkenyl groups; a branched-chain organopolysiloxane that contains vinyl groups; an organopolysiloxane that contains in one molecule at least two silicon-bonded hydrogen atoms; and a hydrosilylation catalyst (see Kokai 2000-198930). Still another example is a curable organopolysiloxane composition comprising: a diorganopolysiloxane that contains diphenylsiloxane units, a branched-chain organopolysiloxane that contains vinyl and phenyl groups; an organopolysiloxane that contains diorganohydrogensiloxy groups; and a hydrosilylation catalyst (see Kokai 2005-76003).
However, the above-mentioned curable organopolysiloxane compositions produce cured products which have either low optical transmittance or poor adherence to substrates and therefore can be easily peeled off from their surfaces.
It is an object of the present invention to provide a curable organopolysiloxane composition that produces a cured body having a high index of refraction, high optical transmittance and hardness, and good adherence to substrates. The invention also provides a semiconductor device that has semiconductor parts of excellent reliability due to coating thereof with a cured body of the aforementioned composition.